Impact absorbing member and head protective member

ABSTRACT

To provide an impact absorbing member for use in vehicles which has excellent energy absorbing capacity and is suitably adapted to absorb impact energy exerted on the head of an occupant in a vehicle cabin to reduce the head injury criteria value in the event of a vehicle collision. An impact absorbing member  1  is a plate-like impact absorbing member  1  made of rigid polyurethane foam and has recesses  3  formed in at least one surface thereof such that the recesses  3  are arranged in parallel along one direction. The shape of each recess  3  on the sectional view in the depth direction of the impact absorbing member  1  is a triangle to have sectional area decreasing toward the deepest point.

FIELD OF THE INVENTION AND RELATED ART STATEMENT

[0001] The present invention relates to an impact absorbing member and,particularly to an impact absorbing member which is suitably adapted toabsorb impact energy exerted on the head of an occupant in a vehiclecabin to reduce the head injury criteria value in the event of a vehiclecollision.

[0002] The followings are impact absorbing members for use in vehicleswhich have been conventionally proposed.

[0003] (1) An impact absorbing member comprising a resin pillar garnishhaving a hollow shape of which a hollow is filled with rigidpolyurethane foam for absorbing impact energy (Japanese PatentH06-42437A).

[0004] (2) A pad member made of foamed material or rubber material (aprior art description of Japanese Patent H08-2358A).

[0005] (3) A cushion body which is made of rigid polyurethane foam andis covered by a shape keeping member of sheet metal having a recessformed therein (Japanese Patent H08-72642A).

[0006] (4) An impact absorbing member which is provided by using agarnish (trim) (Japanese Patent H06-211088A).

[0007] (5) An impact absorbing member made of resin beads which has anumber of ribs formed on one surface (Japanese Patent H07-16867A).

[0008] (6) An impact absorbing member constituted of a polyolefin resinmaterial which has ribs arranged in a lattice shape (Japanese PatentH08-142234A, Japanese Patent H08-295194A).

[0009] The aforementioned conventional impact absorbing members have thefollowing drawbacks, respectively.

[0010] The impact absorbing member disclosed in Japanese utility modelH06-42437A uses the rigid polyurethane foam as the head protectivematerial. However, it has a structure complex with the hollow resinpiece (garnish). Therefore, the rigid polyurethane foam is required tohave low compressive stress of 0.02 to 0.2 MPa. This means that thisdoes not take advantage of characteristics of the rigid polyurethanefoam. The purpose of its concave and convex shape is just to reduce theweight and to keep the strength, and not to improve the energy absorbingcapacity. Therefore, this does not have improved energy absorbingcapacity.

[0011] The impact absorbing member disclosed as a prior art of JapanesePatent H08-2358A is an example of a pad member for absorbing impact madeof foamed material or rubber material. In this example, the pad memberis elastically deformed and thus does not suggest the usage of rigidpolyurethane foam. Portions of a corrugated section attached to avehicle body are extremely thin. To obtain sufficient energy absorbingcapacity, the thickness of the pad member should be large. Accordingly,the cabin space of the vehicle is reduced, thus worsening thecomfortability, the facility of riding, and further the visibility.

[0012] The impact absorbing structure disclosed in Japanese PatentH08-72642A has a concare shape as a whole, but a soft or rigidpolyurethane form itself used as crushing material does not have arecess for improving the energy absorbing capacity. The purpose of arecess formed in the impact absorbing structure is just installation,not improvement of the energy absorbing capacity. In this publication,it is stated that it can not exhibit sufficient energy absorbingefficiency if the entire rigidity is too high or too low. However, thereis no description about specific value and range. It is hard to say thatthis impact absorbing structure securely exhibits excellent energyabsorbing efficiency.

[0013] The impact absorbing member disclosed in Japanese PatentH06-211088A has a structure to be fixed together with a garnish to avehicle body by fasteners so that the garnish is necessary forinstallation of this impact absorbing member. For utilizing the impactabsorbing member as a head protective member, the location adaptabilityis limited, for example, it is not suitably adapted to a side rail. Theimpact absorbing member does not have a concavity or convexity. Thoughit is stated that the impact absorbing member has such a thickness as toabsorb impact energy, there is no description about specific thicknessand hardness. It is also hard to say that the impact absorbing membersecurely exhibits excellent energy absorbing efficiency.

[0014] The impact absorbing member disclosed in Japanese PatentH07-16867A is made of resin beads. When a force is locally exerted on asurface of the impact absorbing member by a spherical body such as ahead dummy, the force focuses on beam portions between the ribs, thusnot obtaining sufficient impact absorbing capacity. If the impactabsorbing member having the aforementioned configuration is made ofrigid polyurethane foam, the beam portions may be broken, thus notobtaining sufficient stroke for absorbing impact energy.

[0015] According to the impact absorbing member disclosed in JapanesePatent H08-142234A and Japanese Patent H08-295194A, the thickness of thelattice-shaped ribs is small such as 0.6 to 1.2 mm. In addition, sincethe ribs made of polyolefin resin material absorbs energy generally bythe bending of the ribs, the impact absorbing member has a drawback thatthe capacity has high dependence of the direction of impact.

[0016] As mentioned above, any one of the aforementioned conventionalimpact absorbing members is not the one whose configuration ispositively devised to obtain the optimal energy absorbing capacity.Accordingly, high energy absorbing capacity can not be imparted to theseimpact absorbing members.

[0017] On the other hand, at pillars and side rails in an automobile,the dimension in thickness has a greater effect on the comfortability inthe cabin and the visibility for the safety. To reduce the head injurycriteria value to protect the occupant without impairing these factors,an impact absorbing member is required which is thin, but can exhibitsufficient energy absorbing efficiency.

[0018] As an impact absorbing member for use in vehicles which can solvethe aforementioned problems and which has excellent energy absorbingcapacity and is suitably adapted to absorb impact energy exerted on thehead of an occupant in a vehicle cabin to reduce the head injurycriteria value in the event of a vehicle collision, an impact absorbingmember has been previously proposed by the applicant of thisapplication, which has a plate-like configuration and is made of rigidpolyurethane foam having compressive stress of a predetermined value ormore, and which has recesses formed in at least one surface thereof(Japanese Patent 2000-6741A) published on Jan. 11, 2000, a correspondingEuropean application of which is EP 967124 A2 published on Dec. 29,1999.

[0019] In this impact absorbing member, walls between adjacent recessesof the impact absorbing member made of rigid polyurethane foam arebroken to absorb impact energy. The broken walls sequentially enter therecesses, thereby obtaining stable energy absorbing capacity. Theentrance of the walls into the recesses provides the stroke forabsorbing energy, thereby sufficiently reducing the head injury criteriavalue suffered by an occupant.

[0020] In this impact absorbing member, it is preferred that the ratioof the volume of the recesses to the sum of the volume of solid portionsmade of the rigid polyurethane foam and the volume of the recesses(hereinafter, sometimes referred to as “recess volume ratio”) is 10 to40%.

OBJECT AND SUMMARY OF THE INVENTION

[0021] Therefore, the object of the present invention is to provide animpact absorbing member for use in vehicles which is an improvement overthe impact absorbing member of Japanese Patent 2000-6741A and which hasexcellent energy absorbing capacity and is suitably adapted to absorbimpact energy exerted on the head of an occupant in a vehicle cabin toreduce the head injury criteria value in the event of a vehiclecollision.

[0022] An impact absorbing member of the present invention is made ofrigid polyurethane foam and has a plate-like shape, and includesrecesses formed in at least one surface thereof to be arranged inparallel along one direction, wherein each recess is formed in such ashape as to have sectional area decreasing toward the deepest point.

[0023] It is preferable that the shape of each recess is acute at thebottom in the depth direction of the impact absorbing member.

[0024] The inventors of this application made efforts for improving theenergy absorbing capacity of the impact absorbing member disclosed inJapanese Patent 2000-6741A. As a result of their efforts, they foundthat the impact absorbing member formed with recesses having such ashape decreasing toward the bottom in the depth direction of the impactabsorbing member, for example having a triangular section along thedepth direction of the impact absorbing direction, has higher energyabsorbing capacity as compared to the impact absorbing member formedwith recesses each having rectangular section even with the same recessvolume ratio. This means that the impact absorbing member formed withsuch recesses can be effectively used for reducing the head injurycriteria value. By this finding, the present invention was accomplished.

[0025] It should be noted that a recess having an acute bottom in thedepth direction of the impact absorbing member of the present inventionwill be sometimes referred to as “acute-bottom recess”. In the presentinvention, the “triangle” on the section view of the recess has the apexangle at the deeper side of the recess.

[0026] According to the present invention, the compressive stress of therigid polyurethane foam constituting the impact absorbing member ispreferably 3×10⁻¹ MPa or more to effectively exhibit the impact energyabsorbing efficiency by the breakage of the rigid polyurethane foamportion between the recesses and also the impact energy absorbingefficiency or capacity by the entrance of the broken portion into therecesses.

[0027] According to the present invention, it is preferable that therecess volume ratio (the ratio of the volume of the recesses to thetotal of the volume of the rigid polyurethane foam portion and thevolume of the recesses of the impact absorbing member) is 3 to 40%.

[0028] When the impact absorbing member has a shape lengthwise in onedirection, the recesses are preferably formed in a portion other thanboth end portions of the impact absorbing member.

[0029] The impact absorbing member of the present invention having theaforementioned construction is suitably used as a head protective memberfor use in vehicles in a state attached to a vehicle body or an interiorequipment such as a head liner and a garnish.

[0030] A head protective member of the present invention is formed in alengthy rectangular shape and is constituted of a rigid polyurethanefoam having hardness of 0.3 MPa or more, a thickness of the headprotective member is 15 to 25 mm and the effective width of portionsmainly absorbing impact is 30 to 40 mm.

[0031] In the present invention, the hardness of material is measured bythe following steps (i)-(iii).

[0032] (i) A sample having a thickness 50 mm×a width 50 mm×a length 50mm (if this size is impossible, an available size may be applied) isprepared from the material.

[0033] (ii) This sample is compressed at a speed of 10 to 50 mm/min in adirection of thickness for a distance of 80% of the original thickness(for a distance of 40 mm when the sample is 50 mm in thickness, i.e. tobe 10 mm).

[0034] (iii) The load when the sample is compressed to be 50% of theoriginal thickness (25 mm of the sample is compressed if the sample is50 mm in thickness) is measured. The hardness (MPa, N/cm²) is obtainedby dividing the measured load by the sectional area.

[0035] When the head protective member has no slit, the effective widthis equal to the actual width of the head protective member. When thehead protective member has a slit, the effective width is the sum ofwidths of solid portions having hardness of 0.3 MPa. It should be notedthat the effective width of portions mainly absorbing impact of the headprotective member of the present invention is referred to just as“effective width”.

[0036] According to the head protective member which is constituted of arigid polyurethane foam having hardness of 0.3 MPa or more and ischaracterized in that the thickness of the head protective member is 15to 25 mm and the effective width is 30 to 40 mm, the HIC value is 800 orless, i.e. excellent energy absorbing capacity can be achieved.

[0037] The HIC value means the head injury criteria value (HIC (d))calculated from acceleration of impact exerted on a dummy in dynamicevaluation tests using dummies. In general, the HIC value of 1000 orless indicates excellent energy absorbing capacity. In carmanufacturers, developments are made to have a HIC value of 800 or lessfor the purpose of increasing the certainty.

[0038] A head protective member of the present invention has, forexample, a slit is formed in the head protective member by hollowing inthe depth direction to extend in the longitudinal direction, such thatthe sum of widths of solid portions other than the slit is set to be 30to 40 cm. In this case, it is preferable that the width of the slit is 5to 20 cm. In addition, it is preferable that the hardness of thematerial constituting the head protective member is 1.2 to 1.6 MPa.

[0039] The head protective member may has a plate-like body withouthaving a slit formed by hollowing in the depth direction. In this case,it is preferable that the hardness of the material constituting the headprotective member is 1.0 to 1.4 MPa.

[0040] The head protective member is suitably used in a vehicle in astate attached to a vehicle body or an interior equipment such as a headliner and a garnish.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041]FIGS. 1a-1 d show an embodiment of the impact absorbing member ofthe present invention, wherein FIG. 1a is a plan view, FIG. 1b is asectional view taken along a line B-B of FIG. 1a, FIG. 1c is a sectionalview taken along a line C-C of FIG. 1a, and FIG. 1d is a perspectiveview.

[0042]FIGS. 2a-2 d show another embodiment of the impact absorbingmember of the present invention, wherein FIG. 2a is a plan view, FIG. 2bis a sectional view taken along a line B-B of FIG. 2a, FIG. 2c is asectional view taken along a line C-C of FIG. 2a, and FIG. 2d is aperspective view.

[0043]FIGS. 3a-3 d show further another embodiment of the impactabsorbing member of the present invention, wherein FIG. 3a is a planview, FIG. 3b is a sectional view taken along a line B-B of FIG. 3a,FIG. 3c is a sectional view taken along a line C-C of FIG. 3a, and FIG.3d is a perspective view.

[0044]FIGS. 4a-4 d show an embodiment of the impact absorbing member ofthe present invention, wherein FIG. 4a is a plan view, FIG. 4b is asectional view taken along a line B-B of FIG. 4a, FIG. 4c is a sectionalview taken along a line C-C of FIG. 4a, and FIG. 4d is a perspectiveview.

[0045]FIG. 5 is a sectional view showing a variation of the impactabsorbing member of the present invention.

[0046]FIG. 6 is a sectional view showing another variation of the impactabsorbing member of the present invention.

[0047]FIG. 7 is a sectional view showing still another variation of theimpact absorbing member of the present invention.

[0048]FIG. 8 is a sectional view showing further another variation ofthe impact absorbing member of the present invention.

[0049]FIGS. 9a, 9 b are sectional views showing examples of the methodof installing the impact absorbing member of the present invention.

[0050]FIG. 10 is a sectional view showing another example of the methodof installing the impact absorbing member of the present invention.

[0051]FIGS. 11a-11 d show an impact absorbing member according to acomparative example, wherein FIG. 11a is a plan view, FIG. 11b is asectional view taken along a line B-B of FIG. 11a, FIG. 11c is asectional view taken along a line C-C of FIG. 11a, and FIG. 11d is aperspective view.

[0052]FIG. 12 is a graph showing the relation between the recess volumeratio and the head injury criteria value in the examples and thecomparative examples.

[0053]FIG. 13a shows a perspective view of an embodiment of the headprotective member of the present invention, and FIG. 13b is a plan viewthereof.

[0054]FIG. 14a shows a perspective view of another embodiment of thehead protective member of the present invention, and FIG. 14b is a planview thereof.

[0055]FIG. 15a shows a perspective view of further another embodiment ofthe head protective member of the present invention, and FIG. 15b is aplan view thereof.

[0056]FIGS. 16a and 16 b are sectional views showing examples of themethod of installing the head protective member of the presentinvention.

[0057]FIG. 17 is a sectional view showing another example of the methodof installing the head protective member of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0058] Hereinafter, embodiments of the present invention will bedescribed with reference to the attached drawing.

[0059]FIGS. 1a through 4d are views showing embodiments of the impactabsorbing member of the present invention, wherein FIGS. 1a, 2 a, 3 aand 4 a are plan views, FIGS. 1b, 2 b, 3 b, 4 b, 1 c, 2 c, 3 c, and 4 care sectional views, and FIGS. 1d, 2 d, 3 d and 4 d are perspectiveviews. Numerical values in FIGS. 1a through 4 a just indicate dimensionsrelated to the embodiments described later, and are not limitative toany of the dimensions of the impact absorbing member of the presentinvention.

[0060] An impact absorbing member 1 shown in FIGS. 1a-1 d has a body 2like a plate made of rigid polyurethane foam and recesses 3 on a topsurface of the body 2. The recesses are formed in a ship's bottomconfiguration, i.e. which is hexagon on the plan view and triangular ona sectional view along a direction perpendicular to the longitudinaldirection. The recesses 3 are arranged in parallel in the widthdirection and adjacent to each other. A rigid polyurethane foam portion4 stands between the adjacent recesses 3, 3. The rigid polyurethane foamportion 4 is broken by impact and the broken portion 4 enters into therecess 3, thereby exhibiting excellent energy absorbing efficiency.

[0061] An impact absorbing member 1A shown in FIGS. 2a-2 d has a body 2Alike a plate and recesses 3A on both surfaces of the body 2A. Therecesses 3A have a similar shape of the recess 3 of the impact absorbingmember 1 shown in FIGS. 1a to 1 d but have a smaller depth. The recessesare formed in both surfaces of the plate body 2A in pairs such that eachpair of recesses 3A are arranged in parallel in the width direction ofthe body 2A. Also in this impact absorbing member 1A, each rigidpolyurethane foam portion 4A between the adjacent recesses 3A, 3A isbroken by impact and the broken portion enters into the recess 3A,thereby exhibiting excellent energy absorbing efficiency.

[0062] An impact absorbing member 1B shown in FIGS. 3a-3 d has a body 2Blike a plate and recesses 3B on a top surface of the body 2B. Therecesses 3B have a square pyramid shape. The recesses 3B are arranged intwo rows in the width direction and in six rows in the longitudinaldirection of the body 2B. Also in this impact absorbing member 1B, eachrigid polyurethane foam portion 4B between the adjacent recesses 3B, 3Bis broken by impact and the broken portion enters into the recess 3B,thereby exhibiting excellent energy absorbing efficiency.

[0063] An impact absorbing member 1C shown in FIGS. 4a-4 d has a body 2Clike a plate and recesses 3C on a top surface of the body 2C. Therecesses have a triangular pyramid shape. The ten recesses 3C arrangedin the width direction and in the longitudinal direction of the body 2C,but this is not limitative. Also in this impact absorbing member 1C,each rigid polyurethane foam portion 4C between the adjacent recesses3C, 3C is broken by impact and the broken portion enters into the recess3C, thereby exhibiting excellent energy absorbing efficiency.

[0064] The rigid polyurethane foam constituting the impact absorbingmember preferably has a compressive stress of 3×10⁻¹ MPa or more. Arigid polyurethane foam having compressive stress less than 3×10⁻¹ MPaprovides insufficient strength of the rigid polyurethane foam portionbetween the recesses. In this case, this portion is easily broken at aninitial stage of application of impact, so the impact absorbing membercan not exhibit sufficient energy absorbing efficiency. The compressivestress of the rigid polyurethane foam is more preferably in a rangebetween 3×10⁻¹ MPa and 4×10⁰ MPa.

[0065] When the recess volume ratio exceeds 40%, the energy absorbingefficiency is insufficient at the initial stage in the same manner asmentioned above. When the recess volume ratio is less than 3%, i.e. toolow, there is insufficient space for the escape of the broken rigidpolyurethane foam portion between the recesses, so the impact absorbingmember can not provide sufficient stroke for absorbing energy. Thismeans that the impact absorbing member can not exhibit sufficient energyabsorbing efficiency at a medium stage and a last stage of theapplication of impact. Accordingly, the recess volume ratio ispreferably 3 to 40%, particularly preferably 5 to 35%.

[0066] As shown in FIGS. 1a-4 d, when the impact absorbing member has alengthy rectangular shape, the recesses are preferably formed in an areaother than the both end portions in the longitudinal direction. The areawhere the recesses are formed preferably has a length of {fraction(5/10)} to {fraction (9/10)} of the entire length about the center inthe longitudinal direction of the impact absorbing member. The ratio ofthe recesses only to the area where the recesses are formed ispreferably 7 to 45%.

[0067] The arrangement of the recesses is not limited to theaforementioned embodiments shown in FIGS. 1a-4 d without space betweenadjacent recesses. The recesses may be arranged at intervals to leaverigid polyurethane foam faces 4D between adjacent recesses 3D, 3D asshown in FIG. 5. However, too large interval W reduces the recess volumeratio and thus loses the energy absorbing capacity. Therefore, theinterval should be 15 mm or less, particularly 10 mm or less. It ispreferable that the adjacent recesses are in contact with each other atthe top surface of the plate-like body.

[0068] When the array pitch of the recesses (the distance between thecenters of the adjacent recesses on the plan view) is more than 80 mm,variations in energy absorbing capacity may be locally caused on thesurface of the impact absorbing member where the recesses are formed.Therefore, the array pitch of the recesses is preferably 80 mm or less.However, since the too small array pitch should make the recess volumeratio insufficient, the array pitch is preferably 5 mm or more.

[0069] There is no specific limitation to the size of each recess, sothe size of each recess may be suitably selected according its shape tosatisfy the conditions of the aforementioned array pitch and said recessvolume ratio.

[0070] The depth of the recesses is suitably selected, according to thearray pitch and the width of the rigid polyurethane foam portion betweenadjacent recesses, within a range satisfying the aforementioned recessvolume ratio. Generally, the depth of the recesses (in case of recessesformed in both surfaces of the plate-like body, the sum of the depths ofthe opposite recesses) is preferably in a range from ⅓ to ¾ of theentire thickness of the impact absorbing member.

[0071] According to the present invention, there is no specificlimitation to the shape of the recess on the plan view, the recesses mayhave any shape such as a parallelogram, a trapezoid, a circle, an oval,and a guitar-shape, in addition to the hexagon as shown in FIGS. 1a-2 d,the square as shown in FIGS. 3a-3 d, the triangle as shown in FIGS. 4a-4d. In every case, the recess should be an acute-bottom recess i.e.having a triangular section or the like. Combinations of recesses havingdifferent shapes on the plan view are also available.

[0072] The impact absorbing member is not limited to the arrangement ofthe recesses, all of which have the same size. The impact absorbingmember may be an impact absorbing member 1E comprising a plate-like body2E and recesses 3E and 3E′ having different depths wherein the recesses3E and the recesses 3E′ are alternately arranged as shown in FIG. 6.Further, as shown in FIG. 7, the impact absorbing member may be animpact absorbing member 1F comprising a plate-like body 2F and recesses3F, each having a triangular section, and recesses 3F′, each having anon-triangular section (rectangular section in FIG. 7), which arealternately formed in the plate-like body 2F.

[0073] The recesses of the impact absorbing member according to thepresent invention is not limited to have triangular sections, and may bea recess 3G having substantially trapezoidal section, a recess 3H, 3I,3J, or 3K having substantially triangular or trapezoidal section havinga curved portion. It is important that any one of the recesses hassectional area decreasing toward the deepest point.

[0074] In case of the acute-bottom recesses, the angle defined by theacute bottom (for example, θ in FIG. 1b) is preferably in a range of 15to 135° in view of the energy absorbing capacity and the design ofrecesses.

[0075] The recesses may be arranged in two or more rows and the way ofthe arrangement is not limited to linear arrangement and may bestaggered arrangement or the like. Suitable design of the arrangement,the shape, and the size of the recesses can control the energy absorbingcapacity and can improve moldability, the directional stability, and thelike of the impact absorbing member.

[0076] To attach the impact absorbing member of the present invention toa vehicle body, for example, as shown in FIG. 9a, the impact absorbingmember 10 of the present invention is mechanically secured to an steelpanel 11 of the vehicle body by tightening screws 12. Alternatively, asshown in FIG. 10, the impact absorbing member 10 of the presentinvention can be attached to an interior equipment (for example, a sheetfor the ceiling) 13 by adhesives 14 or a self-adhesive tape. When theimpact absorbing member is attached to a side rail or the like, thesurface of the impact absorbing member 10 may be pressed and covered bya surfacing material 15 such as an steel panel or resin panel forstabilizing the properties against impact or the like as shown in FIG.9b . Alternatively, the surfacing material 15 may be bonded or stuck tothe impact absorbing member 10, thereby facilitating the installation ofthe impact absorbing member 10 to the vehicle body and furtherincreasing the attachment strength.

[0077] When the impact absorbing member 10 is attached to the vehiclebody, the recesses of the impact absorbing member may be arranged toface the vehicle cabin or the outside of the vehicle cabin. Theattaching direction of the impact absorbing member may be suitablydecided according to the directional stability and stability to theimpact absorbing capacity.

[0078] The impact absorbing member of the present invention will bedescribed in more details with reference to examples and comparativeexamples.

[0079] In the following examples and comparative examples, the energyabsorbing capacity is evaluated by the head injury criteria value (HIC(d)) calculated from acceleration of impact exerted on a dummy indynamic evaluation tests using dummies. In general, the HIC (d) of 1000or less indicates excellent energy absorbing capacity. In carmanufacturers, developments are made to have a HIC (d) of 800 or lessfor the purpose of increasing the certainty.

[0080] In the following examples and comparative examples, each impactabsorbing member was manufactured by preparing a plate-like body made ofrigid polyurethane foam having compressive stress of 1.5 MPa, of whichouter dimension is 210 mm×80 mm×30 mm (thickness), and forming recessesof predetermined shapes in the plate-like body (Comparative Example 1has no recess). The total of the volume of the rigid polyurethane foamportions and the volume of the recesses of the impact absorbing memberis 80 mm (width)×2100 mm (length)×30 mm (thickness)=504000 mm³ (=504cm³). The recess volume ratio is obtained by dividing the volume of therecesses (hereinafter, referred to as “recess volume”) by 504 cm³ and isexpressed by percentage.

EXAMPLES 1-3

[0081] Impact absorbing members as shown in FIGS. 1a-1 d were made. Ineach of the impact absorbing members, two recesses, having dimensionsshown in FIG. 1a and a depth d shown in Table 1, are formed in aplate-like body made of rigid polyurethane foam such that the recessesare arranged in parallel in the width direction and the recess volumeand the recess volume ratio are shown in Table 1.

[0082] For the impact absorbing capacities, the head injury criteriavalues were measured and the results are shown in Table 1. In addition,the relation between the recess volume ratio and the head injurycriteria value is shown in a graph of FIG. 12.

EXAMPLE 4

[0083] An impact absorbing member as shown in FIGS. 2a-2 d was made. Inthe impact absorbing member, two recesses, having dimensions shown inFIGS. 2a, 2 b, are formed in both surfaces of a plate-like body made ofrigid polyurethane foam, respectively, such that the recesses arearranged in parallel in the width direction and the recess volume andthe recess volume ratio are shown in Table 1.

[0084] For the impact absorbing capacity, the head injury criteria valuewas measured and the result is shown in Table 1. In addition, therelation between the recess volume ratio and the head injury criteriavalue is shown in the graph of FIG. 12. TABLE 1 depth of volume recessesvolume of ratio of d recesses recesses HIC Example (mm) (cm³) (%)(note1) (d) 1 10 42  8.3(12.5) 612 2 20 84 16.7(25.0) 600 3 30 12625.0(37.5) 678 4 10(note2) 42  8.3(12.5) 659

EXAMPLES 5, 6

[0085] Impact absorbing members as shown in FIGS. 3a-3 d were made. Ineach of the impact absorbing members, recesses, having dimensions shownin FIG. 3a and a depth d shown in Table 2, are formed in a plate-likebody made of rigid polyurethane foam such that the recesses are arrangedin two rows in the width direction and in six rows in the longitudinaldirection and the recess volume and the recess volume ratio are shown inTable 2.

[0086] For the impact absorbing capacities, the head injury criteriavalues were measured and the results are shown in Table 2. In addition,the relation between the recess volume ratio and the head injurycriteria value is shown in the graph of FIG. 12. TABLE 2 depth of volumeof volume ratio recesses recesses of recesses HIC Example d (mm) (cm³)(%) (note1) (d) 5 20 72 14.3(17) 563 6 25 90 17.9(21) 560

EXAMPLE 7

[0087] An impact absorbing member as shown in FIGS. 4(a)-4(d) was made.In the impact absorbing member, ten recesses, having dimensions shown inFIGS. 4(a), 4(b), are formed in a plate-like body made of rigidpolyurethane foam, such that the ten recesses are arranged in paralleland the recess volume and the recess volume ratio are shown in Table 3.

[0088] For the impact absorbing capacity, the head injury criteria valuewas measured and the result is shown in Table 3. In addition, therelation between the recess volume ratio and the head injury criteriavalue is shown in the graph of FIG. 12. TABLE 3 volume of volume ratiorecesses of recesses HIC Example (cm³) (%) (note1) (d) 7 50 9.9(14) 618

Comparative Example 1

[0089] A plate-like body made of rigid polyurethane foam was made whichis the same as the plate-like body of Example 1, but is formed with norecess. The head injury criteria value was measured and the result isshown in Table 4. In addition the relation between the recess volumeratio (0%) and the head injury criteria value is shown in the graph ofFIG. 12.

Comparative Examples 2-5

[0090] Impact absorbing members as shown in FIGS. 11a-11 d were made. Ineach of the impact absorbing members 20, two rectangular recesses 22having dimensions shown in FIG. 11a and a depth shown in Table 4 areformed in a plate-like body 21 made of rigid polyurethane foam such thatthe recesses are arranged in parallel to leave a space of 10 mm and therecess volume and the recess volume ratio are shown in Table 4.

[0091] For or the impact absorbing capacities, the head injury criteriavalues were measured and the results are shown in Table 4. In addition,the relation between the recess volume ratio and the head injurycriteria value is shown in a graph of FIG. 12. TABLE 4 depth of volumeof volume ratio Comparative recesses recesses of recesses HIC Example d(mm) (cm³) (%) (note1) (d) 1 0 0 0 830 2 5 35  6.9(10) 728 3 10 7013.9(21) 650 4 15 105 20.8(31) 775 5 20 140 27.8(42) 1050

[0092] It was found from the above results that the impact absorbingmembers formed with acute-bottom recesses according to the presentinvention can reduce the head injury criteria value without change inthe recess volume ratio.

[0093] As described in the above, the present invention can provide aenergy absorbing member for use in vehicles which has excellent energyabsorbing capacity and is suitably adapted to absorb impact energyexerted on the head of an occupant in a vehicle cabin to reduce the headinjury criteria value in the event of a vehicle collision.

[0094]FIGS. 13a through 15 b are views showing embodiments of the headprotective member of the present invention, wherein FIGS. 13a, 14 a, and15 a are perspective views and FIGS. 13b, 14 b, and 15 b are plan views.

[0095] The head protective member of the present invention isconstituted of a rigid polyurethane foam having hardness of at least 0.3MPa. The thickness of the head protective member is in a range from 15to 25 mm and the effective width is in a range from 30 to 40 mm. Withthe thickness and the effective width deviating from these ranges, it ishard to achieve the head protective member having a HIC (head injurycriteria) value of 800 or less.

[0096] Concretely, the head protective member of the present inventionhas the following configuration I or II, but not limited thereto.

[0097] I. As shown in FIGS. 13a, 13 b, a head protective member 51 has aslit 51A which is formed by hollowing in the depth direction to extendin the longitudinal direction. In this case, as shown in FIGS. 14a, 14b, the head protective member may have two slits 52A arranged inparallel to each other and, alternatively, may have three or more slits.

[0098] In this configuration, the effective width, that is, the sum ofwidths of solid portions other than the slit(s) (a₁+a₂ in FIG. 1b,a₁+a₂+a₃ in FIG. 2b) is set to be 30 to 40 cm.

[0099] The width of the slit(s) (b₁ in FIG. 1b, b₁, b₂ in FIG. 2b) ispreferably 5 to 20 cm. The width of the solid portions other than theslit(s) (a₁, a₂ in FIG. 13b, a₁, a₂, a₃ in FIG. 14b) is suitably set insuch a manner that the effective width is 30 to 40 cm according to thewidth and the number of the slit(s).

[0100] When a plurality of slits are formed, the respective width of theslits may be the same or different from one another. The width of thesolid portions may also be the same or different from one another.

[0101] According to the present invention, when the head protectivemember has the slit(s), the hardness of the material constituting thehead protective member is preferably 1.2 to 1.6 MPa. In the headprotective member having the slit(s), the configuration of the slit isnot limited to a rectangular shape in its plan view as shown in FIGS.13a to 14 b and may be an oval shape or other shape.

[0102] It should be noted that an actual molded product has thin burrson one of open ends of the slit. There is a possibility that the burrsclose the open end. However, even if one of open ends is closed, it isnot a problem on the performance of the head protective member when thethickness of the closed portion is ¼ or less of the entire thickness.

[0103] II. As shown in FIGS. 15a, 15 b, a head protective member 53 likea plate does not have a slit which is formed by hollowing in the depthdirection. In this case, the effective width is the width of the body.In case of the head protective member 53 having no slit, the hardness ofthe material constituting the head protective member 53 is preferably1.0 to 1.4 MPa.

[0104] To attach the head protective member of the present invention toa vehicle body, for example, as shown in FIG. 16a, the head protectivemember 70 of the present invention is previously formed with a recess70A, a stepped portion 70B, and screw holes and is mechanically securedto an steel panel 71 of the vehicle body by tightening screws 72 intothe screw holes. Alternatively, as shown in FIG. 17, the head protectivemember 70 of the present invention can be attached to an interiorequipment (for example, a sheet for the ceiling) 73 by adhesives 74 or aself-adhesive tape. When the head protective member is attached to aside rail or the like, the surface of the head protective member 70 maybe pressed and covered by a surfacing material 75 such as an steel panelor resin panel for stabilizing the properties against impact or the likeas shown in FIG. 16b. Alternatively, the surfacing material 75 may bebonded or stuck to the head protective member 70, thereby facilitatingthe installation of the head protective member 70 to the vehicle bodyand further increasing the attachment strength.

[0105] The head protective member of the present invention will bedescribed in more details with reference to examples.

EXAMPLE 8

[0106] Head protective members having configurations and dimensionsshown in Table 5 were manufactured by rigid polyurethane foams havinghardness and density shown in Table 5. The respective HIC values of thehead protective members were measured and the results are shown in Table5. TABLE 5 No. of Example 8 9 10 11 Figure(s) which shows the shape theprotective member dimensions of thickness = thickness = 20 mm thickness= 20 mm thickness = 20 mm protective 20 mm a1 = a2 = 15 mm a1 = a2 = a3= 10 mm width = 30 mm member a1 = a2 = 15 mm (effective width =(effective width = (effective width = (effective width = 30 mm) 30 mm)30 mm) 30 mm) b = 15 mm b1 32 b2 = 10 mm b = 10 mm hardness (MPa)* 1.0986 1132  1102  766 (0.097) 1.2 833 830 862 718 (0.110) 1.3 — — — 817(0.116) 1.4 790 801 783 813 (0.122) 1.6 807 804 795 833 (0.134)

[0107] It can be found from Table 5 that head protective members havingexcellent energy absorbing capacity with HIC values of 1000 or less,particularly 800 or less, can be achieved according to the presentinvention.

[0108] As described in the above, the present invention can provide ahead protective member for use in a vehicle which has excellent energyabsorbing capacity and is suitably adapted to absorb impact energyexerted on the head of an occupant in a vehicle cabin to reduce the headinjury criteria value in the event of a vehicle collision.

[0109] The head protective member of the present invention can achievethe HIC value of 800 or less with a simple configuration, therebycontributing the reduction in the manufacturing cost. Therefore, thehead protective member of the present invention is industriallyextremely advantageous.

What is claimed is:
 1. An impact absorbing member made of rigidpolyurethane foam which has a shape of a plate, and which has recessesin at least one surface thereof to be arranged in parallel along onedirection, wherein each recess is formed in such a shape as to havesectional area decreasing toward the deepest point.
 2. An impactabsorbing member as claimed in claim 1 , wherein the shape of eachrecess is acute at the bottom in the depth direction of the impactabsorbing member.
 3. An impact absorbing member as claimed in claim 2 ,wherein the shape of each recess on a sectional view in the depthdirection is a triangle.
 4. An impact absorbing member as claimed in anyone of claims 1 through 3, wherein the compressive stress of the rigidpolyurethane foam is 3×10⁻¹ MPa or more.
 5. An impact absorbing memberas claimed in any one of claims 1 through 4, wherein the ratio of thevolume of the recesses to the total of the volume of the rigidpolyurethane foam portion and the volume of the recesses of the impactabsorbing member is 3 to 40%.
 6. An impact absorbing member as claimedin claim 5 , wherein the impact absorbing member has a shape lengthwisein one direction and wherein the recesses are formed in a portion otherthan both end portions of the impact absorbing member.
 7. An impactabsorbing member as claimed in any one of claims 1 through 6, whereinthe impact absorbing member is used as a head protective member for usein vehicles in a state attached to a vehicle body or an interiorequipment such as a head liner and a garnish.
 8. A head protectivemember which is formed in a lengthy rectangular shape and is constitutedof a rigid polyurethane foam having hardness of 0.3 MPa or more, whereinthe thickness of the head protective member is 15 to 25 mm, and theeffective width of portions mainly absorbing impact is 30 to 40 mm.
 9. Ahead protective member as claimed in claim 8 , wherein said member has aHIC value of 800 or less.
 10. A head protective member as claimed inclaim 8 or 9 , having a slit formed by hollowing in the depth directionto extend in the longitudinal direction, wherein the sum of widths ofsolid portions other than said slit is set to be 30 to 40 cm.
 11. A headprotective member as claimed in claim 10 , wherein the width of the slitis preferably 5 to 20 cm.
 12. A head protective member as claimed inclaim 10 or 11 , wherein the hardness of the material constituting thehead protective member is 1.2 to 1.6 MPa.
 13. A head protective memberas claimed in claim 8 or 9 , wherein the head protective member has aplate-like body without having a slit formed by hollowing in the depthdirection.
 14. A head protective member as claimed in claim 13 , whereinthe hardness of the material constituting the head protective member is1.0 to 1.4 MPa.
 15. A head protective member as claimed in any one ofclaims 8 through 14, wherein the head protective member is used in avehicle in a state attached to a vehicle body or an interior equipmentsuch as a head liner and a garnish.